The present invention relates to an optical pick-up device for performing at least one operation of reproduction, erase, and recording of information upon an information-recording medium.
As the optical pickup device of the above kind, there is a device as shown in FIGS. 14 and 15. FIG. 14 is an illustration showing the construction of the optical pick-up device as viewed sideways. FIG. 15 is an illustration showing the construction of the optical pick-up device as viewed from above. Shown in FIGS. 14 and 15 are a first and a second combination reception and emission devices (for example, hologram laser elements or laser couplers) 101 and 102 emitting laser beams having different wavelengths, a dichroic beam splitter 103 (hereinafter referred to as “DBS”), a collimator lens 104, a riser mirror 105, a quater-wave plate 106, an objective lens 107, an optical disk 108, a monitoring light detection element 109, laser beams 110 and 111 in an effective region, and optical axes 112 and 113 of the laser beams.
In the optical pickup device, as shown in FIG. 14, laser beams 110 in the effective region emitted by the first combination reception and emission device 101 pass through the DBS 103, and are then collimated by the collimator lens 104 and bent perpendicularly by the riser mirror 105, then pass through the quater-wave plate 106, and are finally condensed on a recording surface of the optical disk 108 by the objective lens 107. At this time, several percent of the laser beams 110 in the effective region emitted by the first combination reception and emission device 101 are reflected by the DBS 103 and enter the monitoring light detection element 109, as shown in FIG. 15. The monitoring light detection element 109 outputs an electrical signal corresponding to a light amount of the laser beams incident thereon. The electrical signal drives an unshown automatic power control (“APC”) circuit. The APC circuit controls the output of the first combination reception and emission device 101. Thus the laser beams condensed on the recording surface of the optical disk 108 come to have an appropriate power.
Several percent of the laser beams 111 in the effective region emitted by the second combination reception and emission device 102 pass through the DBS 103, whereas the remainder are reflected by the DBS 103. Laser beams reflected by the DBS 103 travel along the same optical path as that of the laser beams 110 of the first combination reception and emission device 101 and are condensed on the recording surface of the optical disk 108. Laser beams 111 that have passed through the DBS 103 are incident on the monitoring light detection element 109. Thereby as in the case of the output of the first combination reception and emission device 101, the output of the second combination reception and emission device 102 is APC-controlled by the APC circuit. Thus the laser beams condensed on the recording surface of the optical disk 108 come to have an appropriate power.
Laser beams reflected by the optical disk 108 return to the first combination reception and emission device 101 or the second combination reception and emission device 102 via the objective lens 107, the quater-wave plate 106, the riser mirror 105, the collimator lens 104, and the DBS 103. As a result, the laser beams reflected by the optical disk 108 are received by a light-receiving element (not shown) included in the first combination reception and emission device 101 or the second combination reception and emission device 102. As a result, information recorded on the optical disk 108 is detected.
FIG. 16 shows the construction of another background-art optical pickup device as viewed from above. The same parts, shown in FIG. 16, as those shown in FIGS. 14 and 15 are denoted by the same reference numerals as those shown in FIGS. 14 and 15, and description thereof is omitted.
In the optical pickup device shown in FIG. 16, a monitoring light detection element 116 receives laser beams 114 outside of an effective region emitted by the first combination reception and emission device 101. A monitoring light detection element 117 receives laser beams 115 outside of an effective region emitted by the second combination reception and emission device 102. The APC circuit is driven by electric signals outputted from the monitoring light detection elements 116 and 117, thus controlling the output of the first and second combination reception and emission devices 101 and 102.
The DBS 103 has a film for controlling reflection/transmittance characteristics. The film is difficult to form and has a great change in its reflection/transmittance characteristics due to the change in temperature. In addition, the DBS 103 has great variations in dependence on products. Therefore when a plurality of optical pickup devices shown in FIGS. 14 and 15 are manufactured, there may be large variations in the relationship between the light amounts of the laser beams 110 and 111 emitted by the first and second combination reception and emission devices 101 and 102 and the light amounts of the laser beams incident on the monitoring light detection elements 109. Consequently the background-art optical pickup device has a problem that the range of adjustment of the control gain of the APC circuit must be wide.
The speed of recording information on a disk such as CD-R (recordable compact disk) and DVD-R (recordable digital versatile disk) is proportional to the power of the laser beams condensed on the recording surface of the optical disk. Therefore the higher the utilization efficiency of laser beams is, the higher the recording speed is.
The optical pickup device shown in FIGS. 14 and 15 has a problem that the power of the laser beams condensed on the recording surface of the optical disk 108 decreases by the light amount of the laser beams incident on the monitoring light detection element 109 through the DBS 103 and the recordable speed is lowered accordingly. The problem is connected greatly with the performance, quality, and reliability of the optical pickup device.
In contrast, in the optical pickup device shown in FIG. 16, the laser beams 114 and 115 outside the effective region are directed to the monitoring light detection elements 116 and 117. Thus there is no decrease in the power of the laser beams condensed on the recording surface of the optical disk.
The optical pickup device shown in FIG. 16 is not adversely affected by variations of the reflection/transmittance characteristics of the DBS 103. However, the optical pickup device requires two monitoring light detection elements 116 and 117. Thus use of the two monitoring light detection elements 116 and 117 invites the increase in the number of component parts and hence in work to dispose the component parts. Therefore the cost for manufacturing the optical pickup device shown in FIG. 16 is high.
The positions of the monitoring light detection elements 116 and 117 are close to the laser beams 110 and 111 in the effective region. Therefore if the monitoring light detection elements 116 and 117 are dislocated even a little, there is a fear of vignetting of the laser beams 110 and 111 in the effective region. That is, the laser beams 110 and 111 in the effective region may decrease in the amount. Such a situation is connected greatly with the performance, quality, and reliability of the optical pickup device.